Monday, 11 January 2010

The lock nuts allow the boiler fittings to be positioned with more control. They are designed to lock against the boiler bushing. They are made out of 3/8" hex brass stock, and are a bit of an exercise in small scale production lathe work.

Start by chucking up and drilling for the tapping size, in this case for 1/4"-40ME.

Now tap - I did start tapping with the tap held in the tailstock chuck and with the tailstock free to slide along the bed. This allowed me to start off square and straight. Once I had good engagement, I swapped for the tap holder to complete the job.

Pictured below is the final step in 3. Step one - turn to 3/8" diameter for 1/16". Step two - chamfer at 45 degrees to approx 1/32" and then Step three - part to length.

Lather, rinse and repeat (4 times) and we come to the finished article.

The steam outlet is a fitting at the top of the boiler that provides a threaded attachment for the main steam line. It is made of brass; of which we start with a small block on the mill drilling the passages out.

Once that is done we cut out a small bit of waste to make our lives easier when we mount in the lathe.

Using a spring loaded wobbler (actually it is the Taig live center, but it does double duty here) center the part so that the first boss can be turned.

Turning complete now we have to thread 5/16-32 ME - a common size for commercially available nuts and tails.

Threading complete. I also turned a small semicircular groove where the boss meets the square section and chamfered the end.

Here is a shot taken whilst turning the groove on the other boss. This boss is at 90 degrees to the other one and is smaller - in this case 0.250".

This boss gets threaded 1/4-40ME and chamfered as well. Note the piece of soft aluminium protective packing between the chuck jaw and the part.

Saturday, 9 January 2010

The boiler I am making requires a safety valve to bleed excess pressure from the boiler during operation. I am using the same design as the last boiler I made. It consists of a body and a bridge, both made from bronze and a stainless steel pintle that uses a spring to hold a stainless ball against a seat in the body. A pair of stainless rods hold the bridge above the body.

A picture tells a thousand words so here is the finished article:

The body and bridge were both turned on the lathe and then shaped using the CNC mill. Here is a video of this process on the body.

Now we can make a start on the two stainless steel rods that hold the bridge up. Here they are cut roughly to length. The observant amongst you may notice the stupid 22.2250mm dimension which is simply a result of printing out metric drawings originally dimensioned in imperial. To get the rods to length they are faced in the lathe. I also take to opportunity to knock the sharp edges off as well.

I changed the headstock chuck over to a small Jacobs chuck which will hold the rod much more firmly than the normal 3 jaw turning chuck. I will thread the rods from both ends 7BA using a tail-stock die holder.